1. Field of the Invention
The present invention relates to a pulsed-DC ionizer.
2. Discussion of Background
Static charge has been problematic in many industrial fields. Particularly, electrostatic charges on silicon wafers or semiconductor devices have recently been a problem in clean room for semiconductor manufacturing, since they cause production yield loss. As high densification of semiconductor devices progresses, super high cleanliness is required for the production environment, and at the same time the electrostatic resistance of such semiconductor devices tends to be low, whereby the problem of production troubles due to static charge is increasingly problematic.
For controlling static charge, two methods are generally available. Namely, one method is to dissipate static charges by grounding the charged objects, and another method is to neutralize charges with ions. However, in the case of objects having high electric resistance such as wafers or semiconductor devices, it is difficult to dissipate charges by grounding. It has been reported that in such a case, it is effective to employ a method wherein bipolar ions are generated by an ionizer, and the charged objects are neutralized by such ions.
Ionizers which are commonly employed, may be classified into (1) an AC system, (2) a dual-DC system, and (3) a pulsed-DC system.
However, these ionizers have a problem that fine particles are released from the corona discharge electrodes, and they can not be used at a site where such fine particles cause a micro-contamination problem. In addition to such drawback, the above systems (1) and (2) have the following drawbacks.